Transistorized capacitor-discharge system

ABSTRACT

A controlled capacitor-discharge system utilizing a multivibrator source, a full-wave rectifier interposed between the multivibrator and a storage capacitor which is connected directly to the ignition coil. A silicon-controlled rectifier is operative to short the diode bridge and the storage capacitor to send a high-voltage stored energy pulse to the ignition coil and to simultaneously cut off the multivibrator power supply. The silicon-controlled rectifier is controlled in its operation by the points of the distributor on the internal combustion engine so that when the silicon-controlled rectifier is again cut off, the multivibrator will resume oscillation and the capacitor will again store energy.

United States Patent [54] TRANSISTORIZED CAPACITOR-DISCHARGE SYSTEM 3 Claims, 1 Drawing Fig. [52] U.S. Cl 315/209 T, 315/209 CD, 315/209 SC [5 1] Int. Cl 1105b 37/02 [50] Field of Search 315/209 SC, 209 T, 209 CD, 241 P, 209 M [56] References Cited UNITED STATES PATENTS 3,251,351 5/1966 Bowers 123/148 3,312,860 4/1967 Sturm 315/223 3,331,986 7/1967 Hardin et al 315/209 SCR 3,334,619 8/1967 Penn 123/148 3,324,841 6/1967 Kebbon et al.. 123/149 3,032,721 5/1962 Jones 331/113 X 3,516,396 6/1970 Lawson OTHER REFERENCES Van Houten and Schweitzer, A New ignition System For Cars," Electronics, Oct. 5, 1964, pp. 68- 72.

Ward, Transistor ignition, Popular Electronics, June 1964, pp. 33-44 and 8587.

Primary Examiner-Roy Lake Assistant Examiner-Palmer C. Demeo Au0rneyLawrence L. Lerner ABSTRACT: A controlled capacitor-discharge system utilizing a multivibrator source, a full-wave rectifier interposed between the multivibrator and a storage capacitor which is connected directly to the ignition coil. A silicon-controlled rectifier is operative to short the diode bridge and the storage capacitor to send a high-voltage stored energy pulse to the ignition coil and to simultaneously cut 01? the multivibrator power supply. The silicon-controlled rectifier is controlled in its operation by the points of the distributor on the internal combustion engine so that when the silicon-controlled rectifier is again cut off, the multivibrator will resume oscillation and the capacitor will again store energy.

PATENTEDHUV 23 i9?! lll INVENTOR MURRA V GEL LMAN ATTQRNEY TRANSISTORIZED CAPACITOR-DISCHARGE SYSTEM In general, this invention relates to a new and improved transistorized capacitor-discharge system, and more particularly to a transistorized capacitor-discharge system for use with the ignition system of an internal combustion engine.

The ignition system commonly used today is of the single coil interrupter type. This system is based on the principle that the interruption of current through a transformer induces a voltage in the primary winding of the transformer proportional to the inductance of the primary coil and the rate of change of current in the coil. This primary voltage induces a voltage in the secondary winding of the transformer equal to the primary voltage multiplied by the turns ratio of the two windings.

This system operates reasonably well, except that the contacts that do the interrupting do not last because they have to carry the entire ignition current. Thus, although the system is simple and reliable, it fails in many ways to meet the requirements of modern high-speed engines. in fact, the design of the present or Kettering system has not kept pace with the advances made. in other engine areas. The breaker points, for example, have been pushed to their limit to meet the requirements for high-speed engines. These points have a tendency to blue" and pit, thus requiring replacement every 2 to 5,000 miles. Often, the user does not replace the points until or more thousand miles resulting in poor engine performance.

The Kettering system'operates to store energy in the coil when the points are closed and, when the points just start to open the energy stored in the coil induces a voltage into the high-voltage secondary, which secondary voltage produces the spark that fires the spark plug. When the engine is going at a high speed, the input current decreases reducing the high voltage, resulting in misfiring of the engine. The coil current at low speed is very high and must be limited by a ballast resistor. This high current is harmful to the coil and points of the ignition system. As was stated previously, at high speeds the coil current drops off resulting in loss of high voltage to the spark plug. In some instances, the weak high voltage is insufficient to fire the spark plug on some cycles resulting in loss of engine power. This multiple firing or misfiring of the ignition system causes fouling or pitting of the spark plugs and requires their replacement.

A condenser is normally placed across the points to reduce arcing of the points and provide a low-impedance discharge path. Without this condenser the spark would be very weak and the points would burn out. Unfortunately, when the points start to open, a spark is created within the points. This spark eventually starts to carbonize the points and create a pitting effect. When this occurs, the timing of the engine is affected and usually the spark is retarded. The pitting also creates a high-resistance point which prevents the ignition coil from getting the full amount of current it requires to fire the spark plug thus causing hard starting, increased fuel consumption,

. and poor engine performance.

Transistor systems have been utilized in the past to avoid and overcome the problems of standard Kettering systems. 7,

However, these transistor systems have not proved to be adequate substitutes. Thus, prior art transistor systems when used with a regular coil having a turns ratio of 1:100 have caused as much as 380 volts to appear across the transistor. This high voltage could operate to destroy the transistor. There are many ways of protecting the transistor, and examples of these are: Zener diodes, a higher turns ratio in the coil, or three or more transistors in series to achieve greater voltage rating. Although the transistor system appears to be the answer to ignition problems, prior art systems have had many shortcomings, For example, a relay is normally needed between the ignition switch and the transistor unit to supply the necessary current and voltage. Further, a different ignition coil must be used then the one presently found on automobiles with the Kettering system, i.e., the new ignition coil would need a higher turns ratio. Further, because of the high currents passing through the transistor utilized in the prior art systems, large heat sinks must be provided to dissipate the heat in the transistor.

Therefore, it is the general object of this invention to avoid and overcoming the foregoing and other difficulties of prior art practices by the provision of a new and improved transistorizedcapacitor-discharge system.

Another object of this invention is the provision of a new and better transistorized ignition system capable of increasing the point life to more than 40,000 miles.

Still another object of this invention is the provision of a new and improved capacitor-discharge transistorized-ignition system which will eliminate the need for engine tune ups, and spark plug replacements while additionally improving fuel consumption and providing faster starts for an automobile.

A still further object of this invention is the provision of a new and better transistorized-ignition system which will increase the life of a battery while reducing radio interference as found in prior art systems.

A still further object of this invention is the provision of a new and better ignition system which eliminates multiple firing due to point bounce and prevents preignition up to speeds of 15,000 rpm.

Still another object of this invention is the provision of a better capacitor-discharge system utilizing transistors which does not need a ballast resistor and condenser.

Other objects will appear hereinafter.

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

The drawing is a schematic diagram showing the transistorized capacitor-discharge system of the present invention.

The weaknesses of the standard ignition system are eliminated and the advantages previously discussed are gained by utilizing the present system. That is, the present system increases the l2 volts normally available (may be utilized for 6- volt systems) from a car battery to approximately 400 volts. This high voltage is then used to charge up a capacitor. The maximum point current with the present system is less than 0.35 amperes as compared to 8 amperes in prior art systems. The present system utilizes a silicon-controlled rectifier to discharge the capacitor. When the points open, the siliconcontrolled rectifier discharges the capacitor and the pulse generated is applied to the ignition coils. This produces a very fast spark of a much higher voltage then that of a standard system. There is no DC current in the ignition coil as there is with other transistor or standard ignition systems. Therefore the coil cannot over heat nor the points blue. This would occur in the prior art systems because of the high amperage drawn from the battery, whereas, in the present system, the current at low engine speeds is less than 1 ampere with a maximum of 3 amperes at top engine speeds.

In the drawing, the transistorized capacitor discharge system of the present invention is generally designated by the numeral 10. The system is operative from the car battery 12 through the ignition switch 14. Closing of the ignition switch 14 energizes DC to DC converter 16. The converter 16 includes a transformer 18 having three windings 20, 22, and 24. The transformer 18 has a hysteresis loop approaching the shape of a rectangle. Two transistors 26 and 28 are connected with their base terminals to opposite ends of winding 22 and their emitters connected to the ignition switch 14. The transistors operate as switches, one being on while the other is off.

The converter 16 operates as follows. When the ignition switch 14 is turned on, the battery 12 voltage is applied to the emitters of transistors 26 and 28 and through windings 22 and 20 of transformer 18 to the collectors of transistors 26 and 28. The transistors are forwardly biased by resistors 30 and 32 and capacitor 34. Whichever transistor has the most gain is the one which will conduct first. Assuming that transistor 26 is conducting and transistor 28 is cut off, the battery 12 is effectively thus connected across the top half of the center tap primary winding 20 of the transformer 18, This, of course, in-

duces a voltage in all windings of the transformer 18. At the instant transistor 26 starts to conduct, the voltages and currents in the windings assume a maximum level. This condition will-continue to exist until the core of the transformer 18 saturates. Then, the rate of change of flux will drop to zero. During the same time interval, the induced voltages first decrease in value and then become zero. This decrease in voltage first decreases and then removes the base drive to transistor 26. The current then begins to decrease through transistor 26 and causes the flux to be built up in the opposite direction in the primary winding 20. With the voltage of opposite plurality being induced in the winding 20 and, of course, in the other windings in the transformer 18, transistor 28 will start to conduct and the cycle is then repeated.

The forward biasing achieved by resistors 30, 32 and 34 insures that the power supply will start at any temperature, even as low as 40 below zero.

The converter 16 thus produces an AC square wave at the secondary high-voltage winding 24 of the transformer which square wave is in turn rectified by a full-wave rectifier 36 into pulsating DC voltage. This pulsating DC voltage is then applied through a smoothing capacitor 38 to the primary winding 40 of the ignition coil 42. The capacitor 38 also stores this DC energy which in an actual embodimentwas approximately 375 volts. Resistor 44 helps maintain the maximum voltage output and acts as a bleeder when the ignition switch is turned off. A silicon-controlled rectifier 46 is connected to the output of the full wave rectifier 36. The silicon-controlled rectifier 46 acts as an open circuit so long as its control terminal 48 is at zero potential.

In an automobile, there are points 50 connected through a resistor 52 to the ignition switch 14. When the points 50 are closed, resistor 52 allows about one-half an ampere of current to flow through the points. This current helps keep the points clean and the battery 12 sees substantially a resistive load. Upon opening of the points 50, a positive pulse of current is supplied through resistor 54 and forwardly biased diode 56, pulse-shaping capacitor 58 and resistor 60 to the gate 48 of silicon-controlled rectifier 46. Upon receiving this positive pulse, the silicon-controlled rectifier 46 conducts in approximately one microsecond, shorting capacitor 38 to ground. This forces all of the stored energy in capacitor 38 to discharge into the ignition coil 42. This produces a fast hot spark at the terminal of the secondary winding 62 of the ignition coil 42. In prior art systems such as the transistor or Kettering systems, there was produced sputtering or Christmas tree type of spark. However, because most of the energy is dissipated in the first cycle of discharge of the current in capacitor 38, a fast hot spark is created.

At the instant during which capacitor 38 is discharged, the power supply 36 is shorted through the rectifiers. However, this does not harm the converter 16 or its associated transistors 26 and 28 because shorting of the secondary winding 24 merely forces the transistors 26 and 28 into a quiescent state. With this quiescent state, the silicon-controlled rectifier 46 effectively has its power supply turned off and this enables the silicon-controlled rectifier to shutofi". Further, the current through the capacitor 38 and the primary 40 of the ignition coil 42 is in an opposite direction to the charging current and, thus, there is applied a negative voltage on the silicon-controlled rectifier 46 insuring complete turn off. Thus, the silicon-controlled rectifier 46 cannot be made conducting again until another positive pulse is applied to its gate 48.

In order to insure that the silicon-controlled rectifier 46 is not damaged when the current passes in the negative direction, diodes forming the bridge circuit '36 conduct as a short circuit allowing only a maximum of approximately volts to appear on the silicon-controlled rectifier 46 anode.

When the cycle is completed, the power supply turns on because the short circuit is removed and the silicon-controlled rectifier 46 is ready for another firing.

All of the above is accomplished in less than 300 microseconds.

To prevent the silicon-controlled rectifier 46 from conducting by reason of point bounce or transient responses in the system, capacitors 58 and 64 back bias diode 56 and discharge through 54 at a slower rate than the charge time of the system, which charge time is approximately half a millisecond.

Capacitor 66 helps prevent the occurrence of any high-impulse noises that might create radio frequency interference.

lt will be understood that the ordinary ignition coil 42 of an automobile may be utilized in the system of the present invention. Further, the unit can be adapted for use with automobile systems whose voltage might vary between 9 to l6 volts.

it will be noted that the objects of the present invention have been achieved in that a transistorized capacitordischarge system has been provided which eliminates the need for a relay between the ignition system and the transistor unit to supply the necessary current and voltage requirements and, additionally, all of the transistors are operative on substantially low currents so that large heat sinks to dissipate heat from the semiconductor units are not necessary. Further, the system is readily adaptable to a standard ignition coil and is thus readily made for use with any automobile system.

Still further, because of the hot fast spark achieved by utilizing a capacitor-discharge system as provided herein, the sparkplug life will be substantially increased. The unit is operative in the coldest of weathers and, as it draws very little current, the battery life is also increased. Radio interference is eliminated and additionally multiple firing due to balance has been controlled and, in fact, eliminated. No ballast resistor condenser is required by the system of the present invention and the voltage at which the secondary of the ignition coil operates will remain substantially constant up to 15,000 r.p.m. It should be noted that prior art transistor systems were only capable of constant output voltage up to approximately 6,000 r.p.m. and dropped off markedly as they approached 8,000 r.p.m. and were unable to operate without preignition problems beyond this speed. Further, in the Kettering system, as the speed of the motor increased the voltage output of the coil decreased until misfiring at approximately 9,000 to 10,000 r.p.m.

Further, whereas the transistorized-ignition system utilized in the past have been operative at approximately 10 amperes, and Kettering system ignitions drew between 7 amps and onehalf ampere between 0 and 6,000 r.p.m. the transistorized capacitor-discharge system of the present invention is capable of operating between 0.35 amperes and 3 amperes between 0 and 6,000 r.p.m. This low-current requirement substantially increases battery life.

The present invention may be embodied in other specific fonns without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims rather than to the foregoing specification as indicating the scope of the invention.

I claim in my invention:

1. A capacitor-discharge system comprising: a capacitor; a controlled static-switching means; an ignition coil; means connecting the capacitor and switching means in series with the ignition coil; a high-frequency alternating current source connected to the primary winding of a transformer; a full-wave rectifier connected to the secondary of the transformer, the output of said rectifier being directly connected to the capacitor; and gate control means connected to said switching means for providing gate current pulses, said gate control means including second switching means, first capacitance means connected between the second switching means and the staticswitching means, diode means connected between the first capacitance means and the second switching means, resistance means connected in parallel with said diode means, and second capacitance means connected between the first capacitance means and ground.

2. The capacitor-discharge system of claim I wherein the high-frequency alternating current source includes a pair of transistors having commonly connected terminals and forward-biasing means connected to the common terminals to insure low-temperature operation.

3. The capacitor-discharge system of claim 1 wherein the controlled static-switching means is a silicon-controlled rectifier with its cathode connected to ground, and the full-wave rectifier is a diode bridge circuit having one output terminal connected to ground and the other output terminal directly 5 connected to the anode of controlled rectifier.

1. I! i l l 

1. A capacitor-discharge system comprising: a capacitor; a controlled static-switching means; an ignition coil; means connecting the capacitor and switching means in series with the ignition coil; a high-frequency alternating current source connected to the primary winding of a transformer; a full-wave rectifier connected to the secondary of the transformer, the output of said rectifier being directly connected to the capacitor; and gate control means connected to said switching means for providing gate current pulses, said gate control means including second switching means, first capacitance means connected between the second switching means and the staticswitching means, diode means connected between the first capacitance means and the second switching means, resistance means connected in parallel with said diode means, and second capacitance means connected between the first capacitance means and ground.
 2. The capacitor-discharge system of claim 1 wherein the high-frequency alternating current source includes a pair of transistors having commonly connected terminals and forward-biasing means connected to the common terminals to insure low-temperature operation.
 3. The capacitor-discharge system of claim 1 wherein the controlled static-switching means is a silicon-controlled rectifier with its cathode connected to ground, and the full-wave rectifier is a diode bridge circuit having one output terminal connected to ground and the other output terminal directly connected to the anode of controlled rectifier. 